Section 1 of 5Choosing a Fuel
Energy content
- Fuels with a high energy content per kilogram release more energy from a given mass of fuel.
Ease of storage
- Liquid fuels such as petrol are easy to store in tanks, which suits vehicles and filling stations.
Safety
- Liquid petroleum products are relatively safe to store and use compared with some other fuels.
Environmental impact
- Fuels differ in the pollutants and greenhouse gases released when they burn.
Section 2 of 5Uses of Fuels
Uses of Fuels
Transport
- Most road vehicles run on petroleum products such as petrol, diesel and kerosene, all made from crude oil.
Heating
- Gas and oil boilers, open fires, log burners and bottled gas heaters are common ways to heat buildings using fuel.
Electricity
- Fuels burned in power stations heat water to make steam, which drives turbines connected to generators.
Biofuels
- Plant-based fuels such as ethanol can be blended into petrol or diesel to reduce the pollutants released.
Section 3 of 5Calculating Energy Released
1
Identify the fuel's energy content in megajoules per kilogram.
2
Multiply the energy content by the mass of fuel burned in kilograms.
3
Convert megajoules to joules by multiplying by 1 000 000 if required.
4
Remember that only part of this energy is useful, and the rest is wasted.
Section 4 of 5Worked Example
Question
- A fuel has an energy content of 40 MJ per kg.
- Calculate the energy released when 2.0 kg of the fuel is burned completely, in joules.
- Energy released = energy content × mass
- Energy released = 40 × 2.0 = 80 MJ
- Convert1 MJ = 1 × 10⁶ J, so 80 MJ = 80 × 10⁶ J
Answer 8.0 × 10⁷ J released (before any energy is wasted).
Section 5 of 5Exam Checklist & Tips
2.3.1 – Key Points for the Exam
- Fuel A substance whose chemical store of energy is released by combustion.
- Energy content The energy released per kilogram of fuel burned, measured in MJ/kg.
- Combustion Burning a fuel in oxygen to release energy from its chemical store.
- Petroleum A fossil fuel mixture, obtained from crude oil, that includes petrol and diesel.
- Biofuel A fuel made from recently living plant or animal matter.
Common Mistakes
- Confusing energy content in MJ/kg with power output in watts.
- Forgetting to convert megajoules into joules when the answer is required in joules.
- Assuming all the energy released by a fuel is useful energy.
- Describing a fuel as containing heat, rather than energy in its chemical store.